Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$111.79	13.657%	$127.0572	$127.06	$127.05	$127.10
Purchase #2	$146.45	13.174%	$165.7433	$165.74	$165.75	$165.70
Purchase #3	$26.81	4.553%	$28.0307	$28.03	$28.05	$28.00
Purchase #4	$87.96	3.415%	$90.9638	$90.96	$90.95	$91.00
Purchase #5	$31.44	4.722%	$32.9246	$32.92	$32.90	$32.90
Purchase #6	$20.44	5.231%	$21.5092	$21.51	$21.50	$21.50
Purchase #7	$118.32	13.746%	$134.5843	$134.58	$134.60	$134.60
7 purchase totals =	$543.21		$600.8131	$600.80	$600.80	$600.80